Clears the inventory of all tools, armor and weapons, unless item ID is specified, then it'll clear that out as well. but it'll make a breaking noise for each item destroyed. And the amount of damage adds a damage value equal to what you put.

/place <item ID> <amount> <stacked?> <inventory?> <coordinates>Places the <item ID> with the amount of <amount> at the chest you are looking at, or if <inventory?> is true, it will place it in your inventory. <coordinates> will let you place the items in the chest at <coordinates>.

/remove <item ID> <amount> <stacked?> <inventory?> <coordinates>Removes the <item ID> with the amount of <amount> at the chest you are looking at, or if <inventory?> is true, it will remove the item in your inventory. <coordinates> will let you remove the items in the chest at <coordinates>.

/fill <item ID> <inventory?> <coordinates>This command will fill the chest you are looking at with that item, or at the coordinates <coordinates>, and if <inventory?> is true, then it will fill your inventory instead.

/empty <item ID> <inventory?> <coordinates>This command will empty the chest you are looking at with that item, or at the coordinates <coordinates>, and if <inventory?> is true, then it will empty your inventory instead. If there is no item ID, then it will empty everything.

These commands are complete time-savers and can be used with command blocks for adventure maps, and many, many other uses.

Some of these can be accomplished with /blockdata (changing the inv of the chest completely), and /setblock (replacing the chest entirely). However, the rest of the functions are not possible with Player inventories.
(PARTIALY IMPLEMENTED)
EDIT: /empty is pretty much implemented through /clear and /blockdata.